Tyrosinemia is a genetic disorder characterized by elevated blood levels of the amino acid tyrosine. Tyrosinemia is caused by deficiency of tyrosine metabolism, which leads to increased levels of tyrosine and tyrosine products in the body. There are three types of tyrosinemia, classed by the particular enzyme deficiency of the patient. Type 1 tyrosinemia, also known as hepatorenal tyrosinemia, is the most severe form of the disease and is caused by a deficiency of the enzyme fumarylacetoacetate hydrolase, which catalyzes the final step in tyrosine metabolism. Type 1 tyrosinemia can lead to liver and kidney failure, problems affecting the nervous system and increased risk of liver cancer. Type 2 tyrosinemia is caused by a deficiency of the enzyme aminotransferase and affects the eyes, skin and mental development. Type 3 tyrosinemia is the rarest form and is caused by a deficiency of the enzyme 4-hydroxyphenylpyruvate dioxygenase. Type 3 tyrosinemia is characterized by intellectual disability, seizures and intermittent ataxia.
Treatment of tyrosinemia typically involves a diet that is low in phenylalanine and low in tyrosine (low Phe/Tyr). However in children, the low Phe/Tyr diet must also be designed to provide enough of the two amino acids to support growth while avoiding excesses of both. This low Phe/Tyr diet must be consumed for life and compliance is an issue for many. Treatment may also include the administration of nitisinone, a medication that blocks the formation of fumarylacetoacetate.